U-joints are found in two places......in the driveline and at the ends of axles. You probably have an independent front suspension (correct me if I am wrong), so you need to check the driveline. Look at the driveshaft and you will see that the shaft meets the pinion yoke and you see two sections that are shaped like a "U" and meet together at a 90* angle from one another. There will be a cross looking "joint" inside.....this is what folks refer to as a U-joint. The cross has 4 caps, one on every end, and most u-joints have roller pins underneath those caps so that the joint will swivel. When these bearings dry up, the joint will make skweaking sounds that increase in frequency when the vehicle is driven faster. If this is a symptom you are having, then I'd pull the driveshaft and grease the u-joint......some have grease zerks and some require that the cap on the joint be pulled and grease manually inserted.
Here is a good write-up explaining step by step of what I am talking about
:
http://www.stu-offroad.com/misc/driveshaft-1.htm
Mind you, this is for the front driveshaft on a jeep, and if you have a 2wd rear wheel drive vehicle, it might differ slightly....but you should get the idea.